A nondestructive testing technique using an X-ray has been widely used in industry to medicine. An X-ray is electromagnetic waves having a wavelength ranging from about 1 pm to 10 nm (from about 10−12 to 10−8 m). An X-ray having a short wavelength (greater than about 2 keV) is referred to as a “hard X-ray”. In contrast, an X-ray having a long wavelength (ranging from about 0.1 keV to 2 keV) is referred to as a “soft X-ray”.
The absorption contrast method is used for, for example, internal crack inspection of steel materials and security applications, such as baggage inspection. In contrast, for objects to be inspected having a low density, the contrast due to absorption of X-rays is negligibly small. Accordingly, for such objects, an X-ray phase imaging method in which changes in phase caused by a detection object is detected is advantageous.
One of a variety of X-ray phase imaging methods is a refraction contrast method described in PTL 1. The refraction contrast method uses a refraction effect caused by a phase shift in an X-ray induced by a detection object. In the refraction contrast method, an X-ray source having a microfocus is used, and a distance between a detection object and a detector is set to be large. Thus, an image is captured. According to a refraction contrast method, the contour of the image of the detection object is enhanced using the refraction effect of an X-ray caused by the detection object. In addition, unlike other X-ray phase imaging methods, the refraction contrast method does not necessarily require an X-ray having a high interference characteristic, such as synchrotron radiation, since the refraction contrast method uses the refraction effect.